328 occasionaly won't rev or accelerate

I have a 1988 Euro 328. I have had it for 13 years with few difficult problems. It has just had major (engine out) work done on it.

Most of the time it drives extremely well with the usual rapid increase in power as it approaches the rev limit.

However, occasionally when I start it it will not produce any decent amount of power (I estimate < than 100 bhp) and the engine will not rev even with the accelerator on the floor.
Top speed is 60-70mph.
There is no popping or banging or any indication of any type of misfire and the engine is still smooth. I would assume if you lost a whole cylinder bank it would run rough and a huge amount of fuel would be dumped in the exhaust. There is nothing I can do with it running to get it to fix but occasionally when I turn it off and on again it fixes itself. The fault is intermittent, usually it works fine.
I have a rolling road session booked to fault find in the next few days, any hints on where to start looking would be appreciated. My intention is to look at the exhaust gas mixture with the fault present, I am thinking stuck air valve somewhere (auxiliary air valve, solenoid valve) but any other suggestions for the fault finding session would be appreciated.

Please be gentle with me, this is my first post, although I have used the wisdom on ferrarichat many times, it is a great resource.

 

Could it be the fuel pump ?

 

No, if you lose a bank of ignition, it will run perfectly smoothly (but weak). There will be a lot of unburned fuel being dumped into exhaust, but, without a catalytic converter, there will be no negative symptom. Your model (328) has several items that can disable just one bank of the ignition.

 

+1, I have had it happen , it runs perfectly well on one bank - but "won't pull the skin off a rice pudding!"

Its almost certainly ignition related & likely culprits are either a failing coil (or more likely the ignition amplifier module on top of it), just a bad coil-distributor cap ignition lead or possibly something to do with a distributor cap /rotor arm.

Included in the latter might be a failed camshaft/distributor oil seal (look for signs of oil coming out from behind the distributor cap).

It goes without saying to check all the other electrical connections on the coils as well.

 

It is highly likely the frequency valve protection relay.

 

That is how mine acted when I had an 'off and on' FV protection relay. In my 28 years of ownership of my '87 328, I have replaced 3 of those relays. I now carry a spare.

 

In the past I have found one (quick and dirty) way to check the ignition module is to dis-connect the suspect bank module, take the "good" bank module connector and insert into the "suspect" bank module, start her up (briefly - to avoid too much un-burnt fuel being dumped).

If the engine fails to run then likely the original "suspect" bank ignition module may be faulty. If she "runs" the same as before then continue checking the rest of the system.

 

The OP has a euro 328 (K-Jet without Lambda) = no protection relay used.

 

Thanks for the suggestions, all gratefully appreciated. I did not think an engine would run at all smoothly if one ignition bank (halve the cylinders!) is missing so this has been added to my things to check (easy to check for spark on both banks).

When I figure it out I will post the answer.

 

I have discovered the problem is an ignition problem, the bank at the rear of the car is losing its spark at the coil output after working for a few seconds. Will be checking the coil and ignition module on this bank. Has anyone come across a problem where a bank runs for a few seconds and then fails?

regards,

Dave C.

 

The fault has gone hard now which at least means tracing it is easier.

After a long session with more serious equipment I have discovered the problem is one of the ECU pins (pin 14) is not producing the trigger pulse train to generate the sparks. The other one, pin 9 works fine and the engine does run on one bank. Captured on a storage scope, pin 14 produces exactly one pulse when the engine is cranked and then stays at 0V.
Wiring and loading has been considered back to the ECU and is fine (unfortunately).

Does anyone have any experience of taking apart the Micoplex Magneti Morelli MED 806A ECU? Please remember my car is a Euro spec, as far as I can tell the only inputs into the ECU are the TDC sensor and the angular speed sensor, it's a timing box only. Does anyone know of any source of these boxes (I know they will be expensive). Does anyone know of a suitable replacement?

So far I have four options:-

A second hand replacement at £1000 (yet to confirm it is still available)

Some repair companies including one that has worked on a similar ECU before - waiting for quotes from them.

Take it to work (I work for an electronics company) and see if we can figure out the problem and solution. Obviously more information as to what to expect inside would help.

An aftermarket replacement - does anyone know a suitable one?

Any insight greatly appreciated

 

Are you sure its not the BKL3B module, plugged into the coil, maybe either loading the signal or not pulling it high?

Does everything stay the same if you swap over the 2 modules?

 

Could it be a bad flywheel sensor? Aren't there 2 on a 328?

Greg

 

That would affect both banks.

 

I've just traveled the same path with my digiplex playing up on my Euro 3082vi. One of them would shut down when heat stressed.
Decided to replace the internals of both with modern electronics. Do it once and do it properly.

Look up " Ferrari Service of Bedford" David has been very helpful and easy to deal with.
I'm sure he could help with your microplex issue.
Good luck.
-Dave

 

There are several inexpensive secondhand Microplexes on Ebay. I would assume you would need to swap over the EEPROM to maintain the correct timing curve if its from a different car.
If it is the Microplex at fault though the problem might simply be the coil module driver transistor. As the other bank works the difficult-to-repair parts of the circuit (CPU, memory etc) would be OK.

 

I know an Italian guy in Belgium who had a MED 806A in stock. This was april 2015. Don't know if it is still available. Contact me if you are still interested.

 

(If this is still unresolved)

Contrary to what seems logical, a broken TDC sensor can indeed disable just one bank (but only cyl 1-4).

Due to the design of the Microplex, pin 14 (Cyl 1-4) can stop supplying ignition triggers if there is a partial sensor fault with the TDC sensor dropping signals, as example with a broken coil wire or connection cable. You might want to check out your TDC sensor output with a scope while the engine is running to make sure the signal is clean.

If the TDC sensor is good, then have a look at the Microplex circuit board. Left to the LM1815 are four BC327 transistors, the two on the right side (directly next to the LM1815) are the output stages for the trigger signal on pin 14. Measure the base of both transistors to check if there is a trigger signal and to possibly identify the broken transistor. Since you a single pulse on power on the transistors are probably fine.

Should you see no signal at the two transistors then there is a problem with the MC14044 RS-Latch on the left side of the resonator or the driving logic behind it, this is a bit more complex to sort out and requires a scope or logic analyzer, but i am happy to help if you want to tackle this.

I'll publish the circuit diagram for the 806A in the next weeks on Magneti Marelli Dinoplex and Microplex Repair and Restoration Documents, in the meantime you could refer to the diagram for the 120A which is quite similar to the 806A except for some of the MOS down counters due to the different amount of cylinders.

Good luck,
Adrian

 

.....just looking for the simplest problem.....

Have you checked the (vacuum) hose from the plenum to the MicroPlex ? The varying pressure signal is used to control ignition advance --- if it is leaking / absent, you can get a response similar to what you describe.

 

David, if the vacuum hose is missing the Microplex assumes WOT and selects a medium advanced ignition timing, but it should not drop ignitions on one bank as dgmc found out

Best,
Adrian